The invention relates to drilling or boring tools in general, and more particularly to improvements in single-lip solid drilling tools of the type wherein a coolant channel extends longitudinally through the shank of the drilling tool and has a discharge end in the blade-carrying end portion or head of the shank.
In accordance with a prior proposal, the entire end portion of the shank of the single-lip solid drilling tool is made of a hard metal and is designed for the drilling of holes with a diameter of 2.5 to 32 mm. The cutting edge or edges and the guides or margins (if any) are ground directly into and onto the end portion. The end portion is bonded directly to the end of the tubular shank of the drilling tool. This is desirable when the tool is used for the drilling of deep holes, e.g., to drill bores in the barrels of rifles, shotguns and similar weapons. The tubular shank serves as a means for supplying coolant. The utilization of a tubular shank obviates the need for the drilling of a coolant hole in a solid shank, an operation which is complex and expensive if the length of the shank is to suffice for the drilling of bores in the barrels of rifles or in similar workpieces. The coolant holes should not be too large because this would necessitate a reduction of the cross-sectional area or areas of one or more grooves or flutes which serve for evacuation of shavings in the course of the drilling operation. Furthermore, the making of a relatively long small-diameter coolant hole or bore in the shank of an elongated drilling tool necessitates the utilization of a delicate and expensive long and slender drill.
Another drawback of conventional single-lip solid drilling tools is that the sharpening of a blade is extremely complex and expensive so that it is normally advisable to discard the entire tool instead of employing highly skilled persons who are capable of carrying out a satisfactory regrinding operation. Moreover, and even if an expert regrinder is available, the one-piece end portion of a conventional single-lip solid drilling tool cannot be reground more than a few times.
In accordance with another prior proposal, a single-lip solid drilling tool is provided with a separately produced blade which is made of a suitable hard metal and is bonded to the end portion of the shank. This contributes to lower cost of the tool because the entire end portion of the shank need not be made of an expensive high-quality hard metal. However, with the single exception of its lower cost, such drilling tool exhibits the same drawbacks as those of the single-lip drilling tools with blades which are integral parts of hard-metal boring heads, i.e., of one-piece end portions of the tools.
It was further proposed to provide so-called core drills and bore opening or reboring drills with throw-away indexible blades which are made of hard metal and are secured to the end portion of the shank by clamping screws. Such drilling tools cannot be used for the making of holes or bores with a diameter of less than 20 mm.
The utilization of clamping screws to secure blades to the heads of drilling tools is known in connection with so-called spade drills. Reference may be had to U.S. Pat. No. 4,060,335 granted Nov. 29, 1977 to Holloway and Grunsky.